Gas-lift valve

ABSTRACT

An improved form of gas-lift valve apparatus is provided, wherein the check valve portion is relocated upstream of the main shutoff components, relative to injection gas input, to eliminate trapping low pressure between the main shutoff and check valve components. Adjustment means is also provided for selectively adjusting the compression force supplied by the load spring on the main valve stem to permit adjustment of the operating pressure range to correspond with borehole depth and other environmental factors.

United States Patent [72] Inventor Everett 1). McMurry Houston, Tex. [21] Appl. No. 841,046 [22] Filed July 11, 1969 [45] Patented Apr. 20, 1971 [73] Assignee McMurry Oil Tools, Inc.

Houston, Tex.

[54] GAS-LIFT VALVE 15 Claims, 6 Drawing Figs.

[52] US. Cl 137/155 [51] lnt.Cl F04f 1/18 [50] Field oiSearch 137/155, 614.21, 614.2, 614.18; 703/232, 233

[56] References Cited UNITED STATES PATENTS 2,952,268 9/1960 Blum 137/155 3,175,514 3/1965 McMurry 137/155X 3,294,108 12/1966 Thrash 1.37/155 3,439,626 4/1969 Abercrombie 137/155X Primary Examiner-Alan Cohan Attorneys-Arnold, Roylance, Kruger & Durkee, Tom

Arnold, Donald C. Roylance, Walter Kruger, Bill Durkee, Frank S. Vaden,1 1 1 and Edmund F. Bard ABSTRACT: An improved form of gas-lift valve apparatus is provided, wherein the check valve portion is relocated upstream of the main shutoff components, relative to injection gas input, to eliminate trapping low pressure between the main shutoff and check valve components. Adjustment means is also provided for selectively adjusting the compression force supplied by the load spring on the main valve stem to permit adjustment of the operating pressure range to correspond with borehole depth and other environmental factors.

GAS-LIFT vxtva BACKGROUND OF INVENTION This invention relates to gas-lift methods and apparatus for producing oil from subsurface earth formations and the like, and more particularly relates to improved gas-lift valve apparatus.

It is well known that high-pressure gas may be injected into a lower pressure conduit containing oil, and that the injected gas will then expand to carry or lift" a portion of the oil to the surface. It is also well known that one or more gas-lift valves may be located in the borehole at selected locations, and may be adapted to open in response to an injection pressure greater than the pressure within the producing or oil-filled conduit to pass the injection gas into the oil.

The borehole is generally lined with a steel casing, and the production conduit is usually a tubing string concentrically suspended in the casing with the gas-lift valves mounted in a spaced-apart manner at different selected locations along the tubing string. In such a case, the injection gas is supplied into the casing annulus at a selected pressure differential above the operating pressure in the tubing. Alternatively, the-well may be produced through the casing, whereupon the injection gas is supplied to the tubing for release into the casing, and the tubing pressure will therefore necessarily exceed the casing pressure.

It sometimes happens that the injection gas supply pressure will unexpectedly decline, or that the pressure in the production conduit (whether tubing or casing) will unexpectedly increase. Accordingly, it is conventional to include a check valve portion or subassembly within or as a portion of the overall gas-lift apparatus, to prevent backlIow of liquids into the injection conduit. For example, US. Pat. No. 3,175,514 discloses (e.g., col. 9 line 9 et seq.) the conventional arrangement of a check valve located in the normal downstream direction from the main shutoff components and arranged to admit fluid flow from the main valve seat orifice, but to interrupt fluid flow toward the main valve seat orifice.

It may be seen in the aforesaid US. Pat. No. 3,175,514, that a pressure chamber is created between the main valve seat and the check valve seat if both valve shutoff members or stems" are closed at the same time. Originally, this did not create any problem since the check valve portions of equipment of this character were never completely fluidtight whereby the main valve stem would be shielded from pressure in the producing conduit. For various reasons, however, practically all gas-lift valves are made and sold with check portions which achieve a fluidtight seal when closed. Accordingly, it often happens that both valve portions will snap shut in response to a sharp unexpected change in the pressure differential, and that this will produce a low pressure trap between the check and main valve components. When this occurs, neither valve stem can be disengaged from its respective seat member until the valve assembly is removed from the well and disassembled. This can only be done at substantial expense, however, since it is usually necessary to shut in the well completely and to pull" a substantial portion of the producing conduit completely out of the well.

These disadvantages of the prior art equipment and methods are overcome with the present invention, and novel gas-lift valve apparatus is provided herein which includes a fluidtight check valve portionrearranged whereby the main valve stem is continually subjected to the pressure within the producing conduit at all times during gas-lift operations.

SUMMARY OF INVENTION In a preferred embodiment of the present invention, novel gas-lift valve apparatus is provided wherein the arrangement of the check and-main shutoff portions is reversed, and the check valve seat and stem is relocated upstream of the main valve seat and stem. In such an arrangement, a pressure trap can never occur in the manner hereinbefore explained, since each valve stem is spring-loaded in the same direction, although the check valve stem is spring-loaded to close and the main valve stem is spring-loaded toward open position (the main stem nonnally being urged shut by a bellows which is subject to compression by injection gas pressure).

More particularly, the check valve seat is arranged between the injection gas input port (in the valve assembly housing), and the main valve seat, and the check valve stem is located downstream of its seat and spring-loaded to move upstream (of the injection gas input flow) into shutoff engagement with the check valve seat. Furthermore, the bellows is preferably located upstream of the check valve seat, and the main valve stem, which is spring-loaded toward the check valve seat and away from the main valve seat, preferably extends through the annular check valve seat member to a location adjacent the bellows. The check valve stem is preferably an annular member slidably mounted on the main valve stem, and movable independently of the position of the main stem member. In addition, adjustment means is included for adjusting the tension in the main valve stem spring, whereby the operating pressures of the gas-lift valve assembly may more precisely be selected as will hereinafter be explained.

These and other features of the present invention will be apparent from the following detailed description, wherein reference is made to the FIGS. in the accompanying drawings.

DRAWINGS FIG. 1 is a pictorial representation, partly in cross section, of an exemplary gas-lift valve assembly embodying the concept of the present invention.

FIG. 2 is another pictorial representation, also partly in cross section, of a portion of the apparatus depicted in FIG. 1, wherein the components are repositioned to illustrate the effect of a particular pressure condition on the apparatus.

FIG. 3 is another different pictorial representation, again partly in cross section, of the same portion of the apparatus depicted in FIG. 2, wherein the components are differently repositioned to illustrate the different effect produced on the depicted apparatus by a different pressure condition.

FIG. 41 is yet another different pictorial representation, partly in cross section, of the same portion of the same apparatus depicted in FIGS. 2 and 3, wherein the components have been repositioned in yet another manner to illustrate another different effect had on the apparatus by a further change in environmental pressures.

FIG. 5 is a pictorial representation, partly in cross section, of another form of gas-lift valve assembly, also embodying the concept of the present invention, but different from the assembly illustrated in FIGS. 1 I.

FIG. 6 is a pictorial representation, partly in cross section, of another different form of gas-lift valve assembly embodying the concept of the present invention.

DETAILED DESCRIPTION Referring now to FIGS. 1-4, there may be seen several pictorial representations, partly in cross section, of one form of gas-lift valve assembly embodying the present invention, and more particularly illustrating the different positions of the components of the apparatus when subjected to various different environmental pressure conditions. In general, the depicted gas-lift valve assembly may be seen to include a tubular housing 5 threaded at its upper end for interconnection with one end of a conventional connector 2, and a conventional O-ring 32 may be located therebetween to provide a gastight seal. A conventional metal bellows 6 with a bellows end member or plate 22 attached at its upper end may be seento be located in the lower end portion of the housing 5. An annular main valve seat member 19 may be seen to be wedged against an internal shoulder portion of the connector 2, and gastightly fitted thereto by means of an O-ring 31. A main valve stem 11 is provided with a shutoff head 13 adapted for gastight engagement with the main valve seat body 19.

As may also be seen, the main valve seat body 19 may be locked into position against the lower end of the connector 2 by means of a combination stem support and check valve seat member 12 which, in turn, is held in position by engagement between the lower end of the connector 2 and an internal shoulder portion of the housing 5. A suitable O-ring 30 may be included as illustrated to prevent gas seepage about the outside of the check valve seat member 12.

An annular check valve stem 15 may be slidably disposed about the main valve stem 11 and interconnected with a suitable check spring 14 for being urged in the direction away from the main valve seat body 19 into sealing engagement with the shutoff surfaces of the check valve seat member I2. A suitable O-ring 29 may be disposed about the main valve stem 11, between the check valve stem 15, to prevent fluid seepage therebetween.

The lower end of the main valve stem 11 may be seen to be slidably mounted in an annular stem bearing or guide member 16 for coaxial alignment with the orifice of the main valve seat body 19. The guide member, in turn, is secured in the lower end or support section of the check valve seat member 12 by means of a suitable snapring 26, and an O-ring 28 may be seen to be disposed about the main valve stem 11 to prevent gas seepage along its surface. Another O-ring 27 may be seen to be disposed between the inside surface of the check valve seat member 12 and the external surface of the stem guide 16. A suitable gas input port 17 may be seen to be located in the wall of the housing 5, and another input port 18 may be seen to be located in the check valve seat member 12, for admitting gas pressure from outside of the housing 5 into the check valve seat member 12.

The lower end of the main valve stem I1 may be provided with a main stem holder I having threads at its opposite or lower end for rotatable connection with an adjustment nut 8, and a helical mainspring 9 may be disposed about the main stem holder 10 between the adjustment nut 8 and an annular spring retainer 23. As may also be seen, the spring retainer 23 is secured to the upper end of a generally cylindrical mainspring holder 7 which is fixedly attached to the bellows plate 22 at one end, and disposed about the main stem holder 10 at its other end. A suitable snapn'ng 25 may be included for locking the spring retainer 23 into position in the mainspring holder 7. As further illustrated, the mainspring holder 7 is preferably provided with a pair of longitudinal apertures or slots 24 located opposite one another, and adjustment nut 8 is preferably of an elliptical or oblong configuration, whereby it is accommodated within the mainspring retainer 7 but with its ends protruding into the apertures or slots 24. Accordingly, the adjustment nut 8 will be maintained in a generally nonrotatable position, relative to the housing 5, and it is necessary for the main valve stem 11 and main stem holder 10 to be rotated to adjust the location of the adjustment nut 8 on the main stem holder 10. It will be apparent, of course, that the location of the adjustment nut 8 on the main stem holder 10 will determine the compression of the mainspring 9.

Referring again to FIG. I, there may be seen an illustration of the specific positions of the various components of the assembly, when the assembly is in a completely relaxed condition. In this condition, it may be assumed that no dome pressure is supplied to the bellows 6, and that the pressures in the downstream main flow passageway 20 and externally of the housing are both equal to themselves and to ambient or atmospheric pressure. Accordingly, the compressive force of the mainspring 9 will tend to urge the main valve stem 11 downward and out of engagement with the main valve seat body 19, until the downward travel of the main valve stem 11 is arrested by abutting engagement of the lower end of the main stem holder with the upper surface of the bellows plate 22. The check valve stem will also be urged into sealing engagement with the shutoff surfaces of the check valve seat member 12 by the check spring 14.

Referring now to FIG. 2, there may be seen a pictorial representation of the assembly depicted in FIG. 1 when the bellows 6 is charged internally with a suitable operating or dome pressure,'but when the pressures outside of the housing 5 and in the downstream passageway 20 are equal to ambient or atmospheric pressure. Accordingly, the bellows 6 will be expanded or distended longitudinally by its internal or dome pressure, thereby causing the bellows plate 22 to thrust the main stem holder 10 and main valve stem 11 upward oppositely of the force applied to the main valve stem 11 by the compressed mainspring 9, until the shutoff head 13 is urged into sealing engagement with the main valve seat body 19. As may be seen, the check valve stem 15 is positioned by the check spring 14 generally independently of the action of the mainspring 9. Accordingly, the check valve stem 15 remains in sealing engagement with the shutoff surfaces of the check valve seat member 12 irrespective of the position of the main valve stem 11 within the housing 5.

Referring now to FIG. 3, there may be seen another representation of the gas-lift valve assembly wherein the components are depicted in a different position relative to each other. In this illustration, the assembly may be assumed to be disposed in a typical well containing a conventional tubing string (not depicted) suspended in a conventional well casing (also not depicted). It may also be assumed that the tubing is the production conduit, and that the assembly is actuated by injection gas into the casing annulus. Accordingly, the passageway 20 will communicate with the tubing interior, and the outside surface of the housing 5 may be assumed to be exposed to the pressure of the injection gas in the casing annulus.

In the condition represented in FIG. 3, the bellows 6 may be assumed to contain a normal charge of dome pressure, e.g., 600 p.s.i., and the tubing and downstream passageway 20 may be assumed to contain a typical pressure of 575 p.s.i. If the pressure in the casing annulus is less than the tubing pressure of 575 p.s.i., any tubing pressure acting through the orifice of the main valve seat body 19 acts to urge the check valve stem 15 into shutoff engagement with the check valve seat member 12. In addition, the check spring 14 itself will urge the check valve stem 15 shut, provided the casing pressure does not exceed the pressure in the passageway 20 by a differential greater than the strength of the check spring 14.

Since the tubing pressure in the passageway 20 is less than the dome pressure in the bellows 6, the bellows 6 will remain distended to maintain the main valve stem 11 closed with respect to the main valve seat body 19, notwithstanding the main spring 9 which is arranged to urge the main valve stem 11 open. If the casing pressure is gradually increased, however, such pressure will enter the ports 17 and 18, and each time the pressure differential between the casing pressure and the pressure trapped in the space between the check valve stem 15 and the main shutoff head 13 exceeds the relatively small strength of the check spring 14, this will unseat the check valve stem 15 a little to equalize the pressures across the check valve seat member 12. After the casing pressure exceeds the dome pressure, the bellows 6 will begin 'to be compressed longitudinally to thereby draw the bellows plate 22 back away from the threaded end of the main stem holder 10.

Referring now to FIG. 4, there may be seen another pictorial representation of the apparatus depicted in FIGS. 2 and 3, but illustrating the relative positions of the components when the casing pressure is greater than the tubing pressure in the passageway, but not greater than the operating pressure range of the assembly as determined by the position of the adjustment nut 8 on the main stem holder 10. In this illustration, the casing pressure is now at a typical level (i.e. 615 p.s.i.), and thus the casing pressure exceeds the dome pressure. The bellows 6 will now be compressed, and the mainspring 9 will expand sufficiently to pull the shutoff head 13 out of sealing engagement with the main valve seat body 19. This, in turn, will equalize the pressure across the main valve seat body 19, and will accordingly unseat the check valve stem 15, whereby gas will now flow from the casing into the passageway 20.

It should be noted, however, that there will be a pressure differential across the orifice of the main valve seat body 19 during gas flow into the passageway, and that this pressure differential will act in opposition to the mainspring 9 to urge the shutoff head 13 into sealing engagement with the main valve seat body 19. Furthermore, this pressure differential is a function of the space separating the shutoff head 13 and the main valve seat body 19. The position of the adjustment nut 8 on the main stem holder 10 tends to establish the maximum spacing between the shutoff head 13 and the main valve seat body 19, and thus the adjustment nut 8 will determine the operating pressure range of the assembly depicted in FIGS. 2-

In particular, it will be apparent that if the casing pressure rises high enough, the pressure differential across the main valve seat body 19 will also increase until it begins to pull the main valve stem 11 and holder 10 away from the bellows plate 22, notwithstanding the opposition provided thereto by the mainspring 9. Eventually, the main valve stem 11 will be closed, and since the pressure differential across the check valve seat member 12 will now equalize, the check spring 14 will then close the check valve stem 15 as depicted in FIG. 3. Accordingly, it will be apparent that the operating pressure range of the assembly depicted in FIGS. 1-4, will be a casing pressure which is greater than the dome pressure in the bellows 6 as well as the tubing pressure in the passageway 20, but which is less than that sufficient to establish a force from the pressure differential across the main valve seat body 19 which exceeds the strength of the mainspring 9. It will also be apparent that the position of the adjustment nut 8 will determine the pressure differential which is sufficient to close the main valve stem 11 into the main valve shutoff body 19, and since the casing pressure throughout the casing annulus will vary according to the depth of the borehole. Therefore, the adjustment nut 8 will be selectively adjusted to different locations on the main stem holder 10 depending on the borehole depth at which the gas-lift valve assembly is to be located and used, as well as depending on the casing pressures expected to be established and maintained in the borehole. Moreover, this will permit different gas-lift valve assemblies to be opened and closed merely by adjusting the casing pressure in the borehole.

Referring now to FIG. 5, there may be seen a pictorial representation of another form of gas-lift valve assembly which nevertheless embodies the concept of the present invention. In particular, a suitable housing 45 may be seen to be interconnected at its upper end with a conventional connector member 42, as hereinbefore explained, and to contain a suitable bellows 46 and bellows plate 63 in its upper portion. An annular main valve seat body 59 may be seen to be located at the upstream end of a passageway 60 which communicates with the interior of the tubing string (not depicted). A stem guide and seat retainer 41 may be wedged between the lower end of the connector 42 and an internal shoulder portion of the housing 45, to wedge or lock the main valve seat body 59 in position. In addition, a snapring 66 or other suitable locking means may be provided, and O-rings 40 and 43 may be provided as illustrated to confine fluid flow into the passageway 60 to the port 58 and the orifice of the main valve seat body 59.

A main valve stem 51 is slidably supported by the stern guide portion of the stem guide and seat retainer 41 in axial alignment with the main valve seat body 59, and may be provided with a suitable shutoff head 53 at an end and a rotatable adjustment screw 48. A suitable O-ring 44 may be provided to prevent gas or fluid seepage along the surface of the main valve stem 51, but this is not essential.

As may also be seen in FIG. 5, there is an annular check valve seat member 52 disposed adjacent the bellows plate 63, and fixed between an internal shoulder portion of the housing 45 and a snapring 65. A suitable fluid intake port 62 may be provided in the check valve seat member 52, adjacent or near an intake port 57 in the housing 45 and an O-ring gasket 56 may be included between the check valve seat member 52 and the housing 45.

The assembly may further include a suitable cylindricallyshaped check valve stem guide 61, which is threadedly connected at one end to the bellows plate 63, and which extends coaxially through the orifice of the check valve seat member 52. The upper or other end of the check valve stem guide 61 may be seen to be threadedly connected to one end of a tubular mainspring retainer-47 having a substantially closed opposite end portion with a suitable aperture for accommodating the main valve stem 51. A helical mainspring 49 may be disposed concentrically about the main valve stem 51, in the mainspring retainer 47, and may be partially compressed between the head of the adjustment screw 48 and the upper or opposite end of the mainspring retainer 47.

It will be apparent that the compressional force supplied by the mainspring 49 will depend on the strength of the spring 49. However, it will also depend on the relative distance between the head of the adjustment screw 48 and the closed upper end portion of the mainspring retainer 47, and this distance will depend, in turn, on the spacing between the head of the adjustment screw 48 and the threaded end of the main valve stem 51, and on the overall length of the check valve stem guide 61 as may be established by one or more shims 64 adjacent the bellows plate 63.

An annular check valve stem 55 may be slidably mounted on the check valve stem guide 61, downstream of the check valve seat member 52. A small helical check valve spring 54 may be disposed about the stem'guide 61, and between thecheck valve stem 55 and the upper end of the stem guide 61, for urging the check valve stem 55 into shutoff engagement with the check valve seat member 52. An O-ring gasket 50 may be provided as illustrated to prevent gas seepage along the surface of the guide 61.

Referring now to FIG. 6, there may be seen a pictorial representation of another form of gas-lift valve assembly, which is diflerent from that depicted in FlGS. 15, but which nevertheless also embodies the concept of the present invention. In particular, there may be seen a suitable housing 75, having an intake port 87 located in its lower portion, and interconnected at its upper end with a suitable connector 72 as hereinbefore explained. A suitable O-ring '70 may be provided as illustrated, to establish a gastight seal between the housing 75 and the connector 72, and a suitable bellows 76 and bellows plate 93 may be located in the lower end of the housing 75.

An annular main valve seat body 89 may be disposed at the adjacent ends of the housing 75 and connector 72, with its orifice providing a port into the passageway in the connector 72 which communicates with the inside of the tubing string (not depicted). An annular stem guide and seat retainer 71, having one or more suitable ports 88, may be wedged between the end of the connector 72 and an internal shoulder portion of the housing 75 for locking the main valve seat member 89. in place. O-ring gaskets 73 and 74 may be provided for restricting fluid flow into the passageway 90 to the orifice of the main valve seat member 89, and a snapring 77 may be provided to lock the stem guide and seat retainer in position in the housing 75.

As may also be seen in FIG. 6, a cylindrical main valve stem 81, having a threaded lower end portion and a suitable shutofl head 83 at its upper end, may be slidably disposed in the lower guide portion of the stem guide and seat retainer 71 for coaxial alignment with the main valve seat member 89. A suitable adjustment nut 78 having a configuration generally as illustrated may be rotatably mounted on the threaded end of the main valve stem 81, and a helical mainspring 79 may be disposed about the stem 81 between the adjustment nut 78 and the stem guide and seat retainer 71. It will be immediately apparent that the adjustment nut 78 may be shifted selectively along the length of the threaded portion of the main valve stem 81, and that this will selectively vary the compressional force with which the main valve stem 81 is urged away from the main valve seat body 89 by the mainspring 79. A suitable O-ring gasket 91 may be disposed between the main valve stem 81 and the guide portion of the stem guide and seat retainer 71.

As illustrated, an annular check valve seat member 82 may be located in the housing 75 adjacent the port 87 and the bellows plate 93 of the bellows 76, and may be locked into position against an internal shoulder portion of the housing 75 by a snapring 92 or other suitable means. An O-ring 94 or other suitable sealing means may be included as illustrated, to prevent fluid flow between the housing 75 and the check valve seat member 82.

A suitable check valve stem 86 may be slidably disposed in the adjustment nut 78, as illustrated in FIG. 6, with its shutoff head portion 85 confronting the orifice of the check valve seat member 82. A helical check spring 84 or other suitable resilient means may be located in the adjustment nut 78 for urging the check valve stem 86 into shutoff engagement with the check valve seat member 82. As further illustrated, the check valve stem as is preferably provided with a plunger 80 located at the center of its shutofi' head 85 and formed to extend through the orifice of the check valve seat member 82 for abutting engagement with the bellows plate 93. This feature permits the release of high pressure entrapped between the main valve seat body 89 and the check valve seat member 82, since the bellows 76 will distend and unseat the check valve stem 86 from the check valve seat member 82 any time the casing pressure is reduced below the dome pressure in the bellows 76.

It will be apparent from the foregoing that various modifications and variations may be made in the structures and procedures described herein without substantial departure from the essential concept of the present invention. Accordingly, it should be clearly understood that the forms of the invention described herein and depicted in the accompanying drawings, are exemplary only and are not intended as limitations on the scope of the present invention.

lclaim:

l. A gas-lift valve assembly adapted for use in a borehole containing a production conduit and a gas injection conduit, said assembly comprising:

a housing having a gas input port for communication with said injection conduit and a passageway therethrough for connecting said input port with said production conduit;

a main valve seat member disposed in said housing across said passageway;

a main shutoff member movably located generally between said main valve seat member and said input port;

resilient means arranged in said housing to urge said main shutoff member from said main valve seat member;

pressure responsive means arranged in said housing to urge said main shutoff member towards and into sealing engagement with said main valve seat member in opposition to said resilient means; and

check means disposed generally between said main valve seat member and said input port in said housing;

wherein said pressure responsive means comprises bellows means longitudinally distendable under a preselected dome pressure to override said resilient means and to urge said main shutoff member into sealing engagement with said main valve seat member;

wherein said resilient means comprises mainspring means urging said main shutoff member from said main valve seat member and towards said bellows means, and adjustment means for selectively adjusting the tension in said mainspring means;

wherein said main shutotT member comprises;

a main shutoff body having a sealing surface confronting said main valve seat member and adapted for sealing engagement therewith, and

a main stem axially located in said housing and having one end connected to said main shutoff body opposite said sealing surface thereof and having its other end positioned toward said bellows means and threadedly connected to said adjustment means;

and wherein said mainspring means is disposed about said main stem and at least partially compressed between said main shutoff body and said adjustment means.

2. The assembly described in claim 1, wherein said adjustment means is adapted to be selectively spaced from said main shutoff body for selectively adjusting the tension in said mainspring means.

3. The assembly described in claim 2, wherein said check means comprises:

a check seat member disposed in said housing generally between said input port and said main valve seat member,

a check shutoff member disposed between said check seat member and said main valve seat member, and

check spring means for urging said check shutoff member from said main valve seat member and into sealing engagement with said check seat member.

4. The assembly described in claim 3, wherein said check shutoff member is disposed between said main stem and said bellows means.

5. The assembly described in claim 4, wherein said check shutoff member is arranged to be disengaged from said check seat member by said bellows means.

6. The assembly described in claim 3, wherein said check shutoff member is longitudinally movable within said housing independently of said main shutoff member.

7. The assembly described in claim 6, wherein said main shutoff body and stem are movable by said bellows means and mainspring means longitudinally independently of said check shutoff member.

8. The assembly described in claim 7, wherein said check shutoff member is slidably disposed about said main stem.

9. The assembly described in claim 8, wherein said assembly further comprises; carriage means connected with said bellows means and cooperating with said adjustment means to support said mainspring means.

l0. The assembly described in claim 9, wherein said carriage means is disposed at least partially about said main stem, and wherein said adjustment means is threadedly and rotatably connected with said main stem in a manner to selectively compress said mainspring about said main stem in cooperation with said carriage means.

11. The assembly described in claim 10, wherein said adjustment means is a nut threadedly disposed about said main stem.

12. The assembly described in claim 10, wherein said adjustment means is threadedly attached to said main stem as an extension thereof.

13. A gas-lift valve assembly adapted for use in a borehole having a gas injection conduit and a production conduit, said assembly comprising:

an elongate housing adapted for mounting with its axis substantially parallel with said conduits,

said housing having a flow path therein through which the normal downstream flow is from said gas injection conduit to the production conduit;

a first valve seat and cooperating first valve closure upstream of said first seat,

and a second valve seat and cooperating second valve closure downstream of said second seat,

said valve seats being substantially coaxial with each other,

both of said valve closures being in said flow path between said first and second valve seats,

each of said valve closures being movable relative to the other along a common axis of movement,

said first valve member being adapted to close said flow path at said first valve seat by moving in the downstream direction of flow from the injection conduit to the production conduit,

and said second valve member being adapted to close said flow path at said second valve seat by moving in a direction opposite said normal downstream direction and 9 10 said second valve closure being movable to open or close variations in pressure; independently of the position of the hereinafter recited linkage means coaxial with said second valve closure by pressure responsive means; which said pressure responsive means may urge said first a spring at least at times operative upon said first valve valve member to close upon said first valve seat.

member to urge it toward its open direction while al 14. The invention of claim 13, characterized by the addition being yieldable to ermit id fi valve member to of a spring urging said second valve closure toward its closed occupy its closed position; I position a bellows having compressible fluid at a preselected The of clam where! Sald assembly pressure entrapped on one Side thereof and constituting a positioned for gravity to urge said second valve closure toward pressure responsive means including a part movable in closed Posmondirections axial of said two valve seats in response to 

1. A gas-lift valve assembly adapted for use in a borehole containing a production conduit and a gas injection conduit, said assembly comprising: a housing having a gas input port for communication with said injection conduit and a passageway therethrough for connecting said input port with said production conduit; a main valve seat member disposed in said housing across said passageway; a main shutoff member movably located generally between said main valve seat member and said input port; resilient means arranged in said housing to urge said main shutoff member from said main valve seat member; pressure responsive means arranged in said housing to urge said main shutoff member towards and into sealing engagement with said main valve seat member in opposition to said resilient means; and check means disposed generally between said main valve seat member and said input port in said housing; wherein said pressure responsive means comprises bellows means longitudinally distendable under a preselected dome pressure to override said resilient means and to urge said main shutoff member into sealing engagement with said main valve seat member; wherein said resilient means comprises mainspring means urging said main shutoff member from said main valve seat member and towards said bellows means, and adjustment means for selectively adjusting the tension in said mainspring means; wherein said main shutoff member comprises; a main shutoff body having a sealing surface confronting said main valve seat member and adapted for sealing engagement therewith, and a main stem axially located in said housing and having one end connected to said main shutoff body opposite said sealing surface thereof and having its other end positioned toward said bellows means and threadedly connected to said adjustment means; and wherein said mainspring means is disposed about said main stem and at least partially compressed between said main shutoff body and said adjustment means.
 2. The assembly described in claim 1, wherein said adjustment means is adapted to be selectively spaced from said main shutoff body for selectively adjusting the tension in said mainspring means.
 3. The assembly described in claim 2, wherein said check means comprises: a check seat member disposed in said housing generally between said input port and said main valve seat member, a check shutoff member disposed between said check seat member and said main valve seat member, and check spring means for urging said check shutoff member from said main valve seat member and into sealing engagement with said check seat member.
 4. The assembly described in claim 3, wherein said check shutoff member is disposed between said main stem and said bellows means.
 5. The assembly described in claim 4, wherein said check shutoff member is arranged to be disengaged from said check seat member by said bellows means.
 6. The assembly described in claim 3, wherein said check shutoff member is longitudinally movable within said housing independently of said main shutoff member.
 7. The assembly described in claim 6, wherein said main shutoff body and stem are movable by said bellows means and mainspring means longitudinally independently of said check shutoff member.
 8. The assembly described in claim 7, wherein said check shutoff member is slidably disposed about said main stem.
 9. The assembly described in claim 8, wherein said assembly further comprises; carriage means connected with said bellows means and cooperating with said adjustment means to support said mainspring means.
 10. The assembly describeD in claim 9, wherein said carriage means is disposed at least partially about said main stem, and wherein said adjustment means is threadedly and rotatably connected with said main stem in a manner to selectively compress said mainspring about said main stem in cooperation with said carriage means.
 11. The assembly described in claim 10, wherein said adjustment means is a nut threadedly disposed about said main stem.
 12. The assembly described in claim 10, wherein said adjustment means is threadedly attached to said main stem as an extension thereof.
 13. A gas-lift valve assembly adapted for use in a borehole having a gas injection conduit and a production conduit, said assembly comprising: an elongate housing adapted for mounting with its axis substantially parallel with said conduits, said housing having a flow path therein through which the normal downstream flow is from said gas injection conduit to the production conduit; a first valve seat and cooperating first valve closure upstream of said first seat, and a second valve seat and cooperating second valve closure downstream of said second seat, said valve seats being substantially coaxial with each other, both of said valve closures being in said flow path between said first and second valve seats, each of said valve closures being movable relative to the other along a common axis of movement, said first valve member being adapted to close said flow path at said first valve seat by moving in the downstream direction of flow from the injection conduit to the production conduit, and said second valve member being adapted to close said flow path at said second valve seat by moving in a direction opposite said normal downstream direction and said second valve closure being movable to open or close independently of the position of the hereinafter recited pressure responsive means; a spring at least at times operative upon said first valve member to urge it toward its open direction while also being yieldable to permit said first valve member to occupy its closed position; a bellows having compressible fluid at a preselected pressure entrapped on one side thereof and constituting a pressure responsive means including a part movable in directions axial of said two valve seats in response to variations in pressure; linkage means coaxial with said second valve closure by which said pressure responsive means may urge said first valve member to close upon said first valve seat.
 14. The invention of claim 13, characterized by the addition of a spring urging said second valve closure toward its closed position.
 15. The invention of claim 13, wherein said assembly is positioned for gravity to urge said second valve closure toward its closed position. 